An electric power steering (EPS) typically includes components such as steering wheel, column, rack-pinion gear, electric motor actuator etc. The EPS helps the driver to steer a vehicle by providing necessary torque assist. The assist torque is based on driver's applied torque. In a steady-state sense, the driver torque and assist torque counter the rack force generated because of tire-road interaction.
A typical Steer by wire (SbW) system includes a road-wheel actuator (RWA) unit and handwheel (or steering wheel) actuator (HWA) unit. Unlike the EPS, the two units in the SbW are mechanically disconnected and communicate through controlled area network (CAN) interface (or other similar digital communication protocols). The HWA unit receives a rack force signal from the RWA unit to generate an appropriate torque feel for the driver. Alternatively, the handwheel angle and vehicle speed can also be used to generate desired torque feel to the driver. The angle from HWA unit is sent to the RWA unit which performs position control to control rack travel.
For a vehicle with either an EPS or a SbW system, any deviation from the normal vehicle/steering operation would be generally reflected in steering or vehicle signals. Such signals can be used to detect the deviation being experienced by the vehicle at that moment as well as over the time. In the EPS, because the steering wheel is mechanically connected to the rack unit, the driver can experience rack force disturbances due to road surface variation (banking, pothole, road texture) or tire/wheel related phenomenon (wheel imbalance, brake disturbance) directly while steering using the EPS. In the SbW system, it is desirable to provide a notification to the driver in response to the deviation caused by rack force disturbances due to road surface variation (banking, pothole, road texture) or tire/wheel related phenomenon.